Figure 7. Forced Notch signaling in GSCs accelerates age-dependent GSC loss.

(A–C) Three-dimensional reconstructions of images from one-w-old control (A), nos-GAL4-driven N^RNAi (B), and nos-GAL4-driven N^NICD (C) germaria with E-cadherin (E-cad, red), 1B1 (blue, fusomes), and LamC (blue, cap cell nuclear envelopes) labels. A′-C′ show the E-cadherin channel only. (D) Average (avg.) E-cadherin expression at the GSC-niche junction. The number of GSCs analyzed is shown above each bar. *, P<0.05; **, P<0.01. Error bar, mean ± SEM. (E) Relative percentage of GSCs remaining in the germaria of the indicated genotypes at different ages. Flies carrying GFP or GFP^RNAi driven by nos-GAL4 were used as controls. N^NICD was used to increase Notch signaling; RNAi lines were used to suppress the expression of Sxl, shg, or N. The GAL4 control (ctrl) was obtained by crossing the GAL4 line with the w¹¹¹⁸ strain. Line graphs show the maintenance rates of GSCs with age (N, just eclosed; weeks, shown on the x axis). GSC maintenance rates for each genotype were determined by normalizing the average numbers of GSCs at each time point to that in newly eclosed flies. The maintenance rates of both N^NICD-overexpressing and Sxl^RNAi-knock down GSCs were significantly different from those of all the controls (P<0.05), as determined by Wilcoxon Signed-Rank test. Bar graphs indicate the distribution of germaria with 0, 1, 2, or 3 or more GSCs at the indicated weeks. The number of germaria analyzed is shown above each bar. (F) One-w-old nos-GAL4-driven UASp-mCD8-GFP germaria with GFP (gray), 1B1 (red, fusomes), and LamC (red, cap cell nuclear envelopes) labels. F′ shows the GFP channel only. Scale bars in A and F are 5 µm. (G) Notch signaling mediates coordination between GSCs and their niche in response to aging. Aging reduces Notch signaling activity in cap cells, which disrupts niche integrity, and thus affects GSC maintenance; on the other hand, aging up-regulates Notch signaling at the GSC-niche junction (at least in part through Sxl), thereby promoting GSC loss via the suppression of E-cadherin expression. Dark green, cap cell; red, GSC.